1. Field of the Invention
The present invention relates to an arrangement of components fabricated in a semiconductor material with significant design emphasis on the topological arrangement of the components and their interconnections.
2. Related Art
The arrangement of components (e.g., functional blocks) and their interconnections fabricated in a semiconductor material (e.g., on a microprocessor integrated circuit chip) becomes more complicated as the functionality on the chip grows due to the increasing number of transistors integrated on the chip.
Take, for example, the complexity of data dependency checking in the execution unit of a RISC (reduced instruction set computer) microprocessor. Given instructions with two input operands and one output value, as holds for typical RISC instructions, then there are five possible dependencies between any two instructions: two true dependencies, two anti-dependencies, and one output dependency.
Furthermore, the number of dependencies between a group of instructions (such as a group of instructions in a window) varies with the square of the number of instructions in the group, because each instruction must be considered against every other instruction. Complexity is further multiplied by the number of instructions that the processor attempts to decode, issue, and complete in a single cycle, because these actions introduce dependencies, are controlled by dependencies, and remove dependencies from consideration.
True dependencies (sometimes called xe2x80x9cflow dependenciesxe2x80x9d or xe2x80x9cwrite-readxe2x80x9d dependencies) are often grouped with anti-dependencies (also called xe2x80x9cread-writexe2x80x9d dependencies) and output dependencies (also called xe2x80x9cwritexe2x80x94writexe2x80x9d dependencies) into a single group of instruction dependencies. The reason for this grouping is that each of these dependencies manifests itself through the use of registers or other storage locations. However, it is important to distinguish true dependencies from the other two. True dependencies represent the flow of data and information through a program. Anti- and output dependencies arise because, at different points in time, registers or other storage locations hold different values for different computations.
When instructions are issued in order and complete in order, there is a one-to-one correspondence between registers and values. At any given point in execution, a register identifier precisely identifies the value contained in the corresponding register. When instructions are issued out of order and complete out of order, the correspondence between registers and values breaks down, and values conflict for registers. This problem is severe when the goal of register allocation is to keep as many values in as few registers as possible. Keeping a large number of values in a small number of registers creates a large number of conflicts when the execution order is changed from the order assumed by the register allocator.
Anti- and output dependencies are more properly called xe2x80x9cstorage conflictsxe2x80x9d because the reuse of storage locations (including registers) causes instructions to interfere with one another even though the conflicting instructions are otherwise independent. Storage conflicts constrain instruction issue and reduce performance.
In view of the above discussion it becomes clear that implementing data dependency circuits, and register renaming circuits in general, is complex and requires a great deal of semiconductor area. Superscalar RISC processors in particular, strive to simultaneously execute multiple instructions. As this technology develops, chip developers attempt to simultaneously execute more and more instructions. Thus, the required amount of dependency checking increases at an exponential rate.
What is needed is an integrated structure layout (also called a floorplan) of components and interconnections that can efficiently integrate sections of the register renaming circuit (RRC) to conserve semiconductor chip area.
A more detailed description of some of the basic concepts discussed in this application is found in a number of references, including Mike Johnson, Superscalar Microprocessor Design (Prentice-Hall, Inc., Englewood Cliffs, N.J., 1991); John L. Hennessy et al., Computer Architecture-A Quantitative Approach (Morgan Kaufmann Publishers, Inc., San Mateo, Calif., 1990). Johnson""s text, particularly Chapters 2, 6 and 7 provide an excellent discussion of the register renaming and data dependency issues addressed by the present invention.
The present invention is directed to an arrangement of components fabricated on a microprocessor integrated chip with significant design emphasis on the topological arrangement of a Data Dependency Checker (DDC) circuit and a Tag Assignment Logic (TAL) of a Register Renaming Circuit (RRC) circuit and their interconnections to conserve semiconductor real estate.
A basic RRC structure comprises rows and columns of DDC blocks interleaved with TAL blocks laid-out to form a right-angled triangle. The arrangement of the present invention is achieved by flipping several columns of a basic RRC structure so as to open an center channel in the RRC to permit easy routing of TAL outputs.
The layout arrangement of the present invention for the DDC and TAL reduces the distance signals must travel between the DDC and TAL, as well the distance the TAL output signals must travel to reach a set of register port multiplexers (RPM). The specially arranged rows and columns and associated interconnects permits a considerable amount of chip area to be conserved, thus permitting register renaming for many instructions in parallel.